I created a USB bootable version of windows & using WintoUSB. The USB hard drive on which I created it has two partitions: the partition on which I installed the system, and a partition for storage.
I booted into the USB installed system successfully several times. But not suddenly I can no longer boot into it. I noticed for a time that partition was not automatically mounting for some reason, though I was able to find it in disk management. Now it is mounting, but I still can't boot from it.

When I try to boot from it I receive this message:

"The boot selection failed because a required device is inaccessible."

All my files are visible in the directory so I'm guessing the system is still there if I can just access it.